The catalyzed isomerization of alpha-pinene to beta-pinene to which this invention is directed is disclosed in U.S. Pat. No. 3,278,623, the disclosure of which is expressly incorporated herein by reference. The isomerization is carried out in the presence of a transitory hydrogen acceptor catalyst using hydrogen gas as a co-catalyst. A preferred hydrogen acceptor catalyst is a Group VIII metal on an alumina support.
Such isomerization process also produces acidic byproducts, hydrogenation products, and polymerization products of the initial alpha-pinene feed supply. These related byproducts decrease the selectivity of the Group VIII catalyst for beta-pinene formation. Kaiser in U.S. Ser. NO. 576,718, now U.S. Pat. No. 3,974,103, discloses a method for substantially suppressing the acidic byproduct formation by subjecting the alumina-supported Group VIII catalyst to a neutralization treatment in order to neutralize the acid functionality displayed by the catalyst.
Heretofore, Inami et al reported that contacting 1-butene with a gold catalyst caused isomerization to 2-butene, and contacting 1-butene with a palladium catalyst caused dehydrogenation. (Isomerization and Dehydrogenation of Butene Catalyzed by Nobel Metals and Their Alloys, Journal Catalysis, Vol. 13, pp. 397-403 (1969)). These authors further reported that up to 40 atom-percent palladium can be alloyed with the gold without undue loss of isomerization activity of 1-butene to 2-butene.
In "Olefin Hydrogenation Catalyzed by Supported and Unsupported Mixed Metals," Journal Catalysis, Vol. 26, pp. 92-96 (1972), Inami et al reported that a palladium-gold unsupported catalyst is useful in catalytically hydrogenating cyclopentene and that an alumina-supported palladium-gold (up to 25 atom-percent gold) catalyst is useful in catalytically hydrogenating benzene.
It is an object of the present invention to increase the percent conversion (specificity) of a Group VIII catalyst for the formation of beta-pinene and at the same time retain high selectivity of the catalyst for beta-pinene formation.
For purposes of this application, selectivity is measured as a function of all byproducts formed during the isomerization process, and is calculated as follows: ##EQU1## By suppressing by-product formation, selectivity is increased. Specificity is measured as a function of the degree of conversion of alpha-pinene to beta-pinene during the isomerization process and is calculated as follows: ##EQU2##